As one of technologies to increase the communication speed of mobile stations located at cell edges, DC-HSDPA using existing HSDPA (High Speed Downlink Packet Access) has been examined in Release 8 of 3GPP (3rd Generation Partnership Project). DC-HSDPA uses two adjacent carrier frequency bands (each of which is 5 MHz) within the same frequency band in order to increase the downlink speed. The general idea of DC-HSDPA, which has been currently examined in 3GPP, is explained hereinafter. Note that the details of DC-HSDPA technique are explained in 3GPP Technical Specification (Non-patent literatures 1 to 3).
In DC-HSDPA, a first serving HS-DSCH cell is simply referred to as “serving HS-DSCH cell”. Further, a second serving HS-DSCH cell is referred to as “secondary-serving HS-DSCH cell”. The second serving HS-DSCH cell is dependently formed on condition that the first serving HS-DSCH cell is already generated. Note that the serving HS-DSCH cell may be also referred to as “primary carrier” or “base carrier”. Meanwhile, the secondary-serving HS-DSCH cell may be also referred to as “secondary carrier” or “extended carrier”.
The first serving HS-DSCH cell can use all the HSDPA physical channels (which are described later) for communication with mobile stations. In contrast to this, the second serving HS-DSCH cell of DC-HSDPA uses part of the control information of the first serving HS-DSCH cell for communication with mobile stations. By using this common control information, the second serving HS-DSCH cell can be operated by just setting some of the physical channels of HSDPA (which are described later), and thereby preventing the use efficiency of radio resources from being lowered due to the redundant transmission of the control information.
In this specification, in order to clearly distinguish between these two serving HS-DSCH cells, the first serving HS-DSCH cell is referred to as “primary-serving HS-DSCH cell”. Further, in the following explanation, the primary-serving HS-DSCH cell and the secondary-serving HS-DSCH cell may be also referred to as simply “primary cell” and “secondary cell” respectively.
FIG. 23 shows physical channels used to perform packet communication using DC-HSDPA between a base station 91 supporting DC-HSDPA and a mobile station 92. HS-PDSCH is a downlink physical channel for data transmission, and transfers a transport channel HS-DSCH. HS-SCCH is used for transmission of downlink signaling information about HS-DSCH transfer.
HS-DPCCH is an uplink physical channel used to transmit feedback information about HS-DSCH transfer from the mobile station 92 to the base station 91. This feedback information includes an ACK response regarding a hybrid ARQ (Automatic repeat-request), and a CQI (channel Quality Indication). When a secondary cell is used, information of both the primary cell and the secondary cell is multiplexed in the feedback information in HS-DPCCH of the primary cell.
The uplink DPCH and the downlink DPCH are used for transmission/reception of control information about DC-HSDPA, uplink/downlink power control, reporting of measurement information to a base station, and the like. Further, in addition to the uplink DPCH, E-DCH can be also used for uplink communication. The details of E-DCH are explained in 3GPP Technical Specification (Non-patent literature 4). Note that other common channels indispensable for the generation of a primary cell and a secondary cell (such as P-CPICH, SCH, P-CCPCH and S-CCPCH) are also used.
The formal names of the physical channels and transport channels, which are shown in abbreviated names in the above explanation, are shown below.    P-CPICH: Primary Common Pilot Channel    DPCH: Dedicated Physical Channel    HS-DPCCH: Dedicated Physical Control Channel (uplink) for HS-DSCH    HS-DSCH: High Speed Downlink Shared Channel    HS-PDSCH: High Speed Physical Downlink Shared Channel    HS-SCCH: Shared Control Channel for HS-DSCH    P-CCPCH: Primary Common Control Physical Channel    S-CCPCH: Secondary Common Control Physical Channel    SCH: Synchronization Channel    E-DCH: Enhanced Dedicated Channel
Further, in 3GPP Release 9, MC-HSDPA (Multi-Carrier HSDPA operation) has been examined as a method for extending DC-HSDPA. MC-HSDPA uses a combination of carrier frequency bands belonging to different frequency bands, i.e., a combination of carrier frequency bands that are not adjacent to each other but are away from each other is used for a primary cell and a secondary cell. The details of MC-HSDPA are explained in Non-patent literature 5.